chr1-45500334-T-G

Variant names:

• chr1-45500334-T-G
• rs574983400
• NM_015506.3:c.2T>G

Variant summary

Our verdict is Pathogenic. The variant received 20 ACMG points: 20P and 0B. PVS1 PS1_Moderate PM2 PP5_Very_Strong

The NM_015506.3(MMACHC):​c.2T>G​(p.Met1?) variant causes a start lost change. The variant allele was found at a frequency of 0.00000137 in 1,461,782 control chromosomes in the GnomAD database, with no homozygous occurrence. In-silico tool predicts a pathogenic outcome for this variant. Variant has been reported in ClinVar as Likely pathogenic (★★).

• Frequency:
  • Genomes: not found (cov: 32)
  • Exomes 𝑓: 0.0000014 (0 hom.)
• Consequence: MMACHC NM_015506.3 start_lost
• Clinical Significance: Pathogenic/Likely pathogenic criteria provided, multiple submitters, no conflicts P:3
• Conservation: PhyloP100: 4.51

Genes affected

MMACHC (HGNC:24525): (metabolism of cobalamin associated C) The exact function of the protein encoded by this gene is not known, however, its C-terminal region shows similarity to TonB, a bacterial protein involved in energy transduction for cobalamin (vitamin B12) uptake. Hence, it is postulated that this protein may have a role in the binding and intracellular trafficking of cobalamin. Mutations in this gene are associated with methylmalonic aciduria and homocystinuria type cblC. [provided by RefSeq, Oct 2009]

ACMG classification

Our verdict: Pathogenic. The variant received 20 ACMG points.

• PVS1: Start lost variant, next in-frame start position is after 19 pathogenic variants. Next in-frame start position is after 58 codons. Genomic position: 45507446. Lost 0.203 part of the original CDS.
• PS1: Another start lost variant in NM_015506.3 (MMACHC) was described as [Pathogenic] in ClinVar as 203823
• PM2: Very rare variant in population databases, with high coverage
• PP5: Variant 1-45500334-T-G is Pathogenic according to our data. Variant chr1-45500334-T-G is described in ClinVar as [Likely_pathogenic]. Clinvar id is 557424.Status of the report is criteria_provided_multiple_submitters_no_conflicts, 2 stars.

Transcripts

RefSeq

Gene	Transcript	HGVSc	HGVSp	Effect	Exon rank	MANE	Protein	UniProt
MMACHC	NM_015506.3	c.2T>G	p.Met1?	start_lost	Exon 1 of 4	ENST00000401061.9	NP_056321.2
MMACHC	NM_001330540.2	c.-221T>G		5_prime_UTR_variant	Exon 1 of 4		NP_001317469.1

Ensembl

Gene	Transcript	HGVSc	HGVSp	Effect	Exon rank	TSL	MANE	Protein	Appris	UniProt
MMACHC	ENST00000401061.9	c.2T>G	p.Met1?	start_lost	Exon 1 of 4	2	NM_015506.3	ENSP00000383840.4
MMACHC	ENST00000616135.1	c.-170T>G		upstream_gene_variant		2		ENSP00000478859.1

Frequencies

GnomAD3 genomes Cov.: 32

GnomAD4 exome AF: 0.00000137 AC: 2 AN: 1461782 Hom.: 0 Cov.: 30 AF XY: 0.00000275 AC XY: 2 AN XY: 727196

African (AFR) AF: 0.00 AC: 0 AN: 33480

American (AMR) AF: 0.00 AC: 0 AN: 44722

Ashkenazi Jewish (ASJ) AF: 0.00 AC: 0 AN: 26136

East Asian (EAS) AF: 0.00 AC: 0 AN: 39698

South Asian (SAS) AF: 0.00 AC: 0 AN: 86252

European-Finnish (FIN) AF: 0.00 AC: 0 AN: 53420

Middle Eastern (MID) AF: 0.00 AC: 0 AN: 5684

European-Non Finnish (NFE) AF: 0.00000180 AC: 2 AN: 1112006

Other (OTH) AF: 0.00 AC: 0 AN: 60384

GnomAD4 genome Cov.: 32

ClinVar

Significance: Pathogenic/Likely pathogenic

Submissions summary: Pathogenic:3

Revision: criteria provided, multiple submitters, no conflicts

Submissions by phenotype

Cobalamin C disease Pathogenic:3

Apr 06, 2023

Labcorp Genetics (formerly Invitae), Labcorp

Significance: Pathogenic

Review Status: criteria provided, single submitter

Collection Method: clinical testing

For these reasons, this variant has been classified as Pathogenic. ClinVar contains an entry for this variant (Variation ID: 557424). Disruption of the initiator codon has been observed in individuals with methylmalonic aciduria and homocystinuria (PMID: 16311595, 17768669, 19760748, 28693988). This variant is not present in population databases (gnomAD no frequency). This sequence change affects the initiator methionine of the MMACHC mRNA. The next in-frame methionine is located at codon 58. -

Mar 24, 2018

Counsyl

Significance: Likely pathogenic

Review Status: no assertion criteria provided

Collection Method: clinical testing

This submission and the accompanying classification are no longer maintained by the submitter. For more information on current observations and classification, please contact variantquestions@myriad.com. -

Apr 11, 2023

Genome-Nilou Lab

Significance: Likely pathogenic

Review Status: criteria provided, single submitter

Collection Method: clinical testing

- -

Computational scores

Source: dbNSFP v4.3

Name	Calibrated prediction	Score	Prediction
BayesDel_addAF	Pathogenic	0.60	D
BayesDel_noAF	Pathogenic	0.65
CADD	Uncertain	25
DANN	Uncertain	0.98
DEOGEN2	Benign	0.076	T
Eigen	Uncertain	0.61
Eigen_PC	Uncertain	0.61
FATHMM_MKL	Uncertain	0.89	D
LIST_S2	Uncertain	0.90	D
M_CAP	Pathogenic	0.95	D
MetaRNN	Pathogenic	0.99	D
MetaSVM	Pathogenic	1.0	D
PhyloP100		4.5
PROVEAN	Benign	-1.4	N
REVEL	Pathogenic	0.79
Sift	Pathogenic	0.0	D
Sift4G	Pathogenic	0.0	D
Polyphen		0.99	D
Vest4		0.95
MutPred		0.99		Loss of ubiquitination at K4 (P = 0.0342);
MVP		0.99
ClinPred		1.0	D
GERP RS		5.8
PromoterAI		-0.20	Neutral
Varity_R		0.99
gMVP		0.76
Mutation Taster		=3/197	disease causing (ClinVar)

Splicing

Name	Calibrated prediction	Score	Prediction
SpliceAI score (max)		0.0		Details are displayed if max score is > 0.2

Find out detailed SpliceAI scores and Pangolin per-transcript scores at spliceailookup.broadinstitute.org

Publications

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Other links and lift over

dbSNP: rs574983400; hg19: chr1-45966006;